Light can be represented as electromagnetic fields which vary sinusoidally and orthogonal to the direction of propagation as shown in FIG. 1. [where the direction of propagation is along the Z-axis.]
For the purposes of this invention it is only the electric field component of the wave which will interact with matter and produce relevant phenomena. An electric field is simply the force per unit electric charge in a region of space. Equivalently, if an electric charge were in a region of space occupied by an electric field it would experience a force equal to the electric field times the magnitude of the charge.
Electric fields can be represented mathematically as vector quantities indicating their magnitude and direction at a specific point or in a given region of space. FIG. 1A is the electromagnetic wave in FIG. 1, but with the view looking down the axis of propagation, the Z-axis. FIG. 1-A shows some possible orientations of the electric field. These are only some possibilities. Any orientation in the plane normal to the direction of propagation is possible. That plane is represented as the plane that the circle in FIG. 1A occupies.
As light, an electromagnetic wave, propagates, the behavior of the electric field in space and time is determined by Maxwell's equations, which are a set of equations defined by James Clerk Maxwell which constitute the physical laws of electromagnetism. Maxwell's equations have solutions for travelling waves where the electric field varies along an axis as in FIG. 1, varies in a circular of elliptical manner, or varies randomly.
The orientation of the electric field vector and how it changes with time is known as the state of polarization of the electromagnetic wave or just simply the polarization of the light. If the electric field is confined to a single axis as in FIG. 1 it is said to be linearly polarized. In FIG. 1 it is linearly polarized in the X or vertical direction. Since the electric field at any given moment is confined to a plane parallel to the direction of propagation and a plane is two dimensional, there are only two possible polarization states for light. We can think of them as horizontal and vertical. Although in physics and mathematics the two unique polarization states used are sometimes fight and left circular polarization, these states are simply combinations of vertical and horizontal states that vary in time in the fight way to represent an electric field that rotates in a circular clockwise manner or counterclockwise as the wave propagates. For our purposes we shall speak in terms of vertical and horizontal linearly polarized states knowing that everything we present in this invention is also true if we replace these states with fight and left circularly polarized states.
Some materials act as polarizers. If randomly polarized light enters into a slab of finite thickness of polarizing material with the material's polarization oriented say in the vertical direction, the horizontally polarized portion of the incident light is absorbed and the vertically polarized portion is allowed to pass through the material. The result is that the light emanating out of the polarizing material is polarized in the vertical direction thus polarizing materials polarize light.
The making of sheet polarizers, polarizing material on large sheets of substrates, was pioneered by Edwin H. Land and more by John F. Dreyer. The polarizing layer on these substrates is called a dichroic layer. The phenomena of polarizers and polarizing sheets relate to this invention.
There are also techniques of depositing thin layers of metal, metal oxides, or conducting polymer materials onto substrates. These layers do not polarize light but they act as partial reflectors. They reflect only part of the light that is shined upon them. When you look at one of these layers on a clear substrate you can see objects on the other side and you can also see your reflection. As the thickness of these layers is increased the reflective property increases and the transparent property decreases. The phenomena of partial reflection relates to this invention.
Polarizing layers and conducting layers can be combined as parallel elements onto substrates to produce laminates that can be used for various purposes. Various prior art techniques have been developed to produce such combinations of parallel elements for various purposes. See U.S. Pat. No. 2,776, 598 to Dreyer, U.S. Pat. Nos. 2,788,707 and 2,997,390 to Land, U.S. Pat. No. 4,025,688 to Nagy et al., U.S. Pat. No. 5,347,644 to Sedlmayr et al., and U.S. Pat. No. 3,248,165 to Marks et al.
This invention employs polarizing and reflective parallel elements combined on an optical substrate of specific design parameters, governed by the operation of the invention.
An object of the proposed invention is to produce and display a three dimensional image of a single person or object.
Various prior art techniques and apparatus have been heretofore proposed to present three dimensional images on a viewing screen using a stereographic technique such as on a polarization conserving motion picture screen.
See U.S. Pat. No. 4,955,718 to Jachimowicz, et al., U.S. Pat. No. 4,963,959 to Drewio, U.S. Pat. No. 4,962,422 to Ohtomo, et al., U.S. Pat. No. 4,959,641 to Bess, et al., U.S. Pat. No. 4,957,351 to Shioji, U.S. Pat. No. 4,954,890 to Park, U.S. Pat. No. 4,945,408 to Medina, U.S. Pat. No. 4,936,658 to Tanaka, et al., U.S. Pat. No. 4,933,755 to Dahl, U.S. Pat. No. 4,922,336 to Morton, U.S. Pat. No. 4,907,860 to Noble, U.S. Pat. No. 4,877,307 to Kalmanash, U.S. Pat. No. 4,872,750 to Morishita, U.S. Pat. No. a4,853,764 to Sutter; U.S. Pat. No. 4,851,901 to Iwasaki, U.S. Pat. No. 4,834,473 to Keyes, et al., U.S. Pat. No. 4,807,024 to McLaurin, et al., U.S. Pat. No. 4,799,763 to Davis, U.S. Pat. No. 4,772,943 to Nakagawa, U.S. Pat. No. 4,736,246 to Nishikawa, U.S. Pat. No. 4,649,425 to Pund, U.S. Pat. No. 4,641,178 to Street, U.S. Pat. No. 4,541,007 to Nagam, U.S. Pat. No. 4,523,226 to Lipton, et al., U.S. Pat. No. 4,376,950 to Brown, et al., U.S. Pat. No. 4,323,920 to Collendar, U.S. Pat. No. 4,295,153 to Gibson, U.S. Pat. No. 4,151,549 to Pautzc, U.S. Pat. No. 3,697,675 to Beard, et al.
These techniques and apparatus involve the display of polarized or color sequential two-dimensional images which contain corresponding right eye and left eye perspective views of three dimensional objects. These separate images can also be displayed simultaneously in different polarizations or colors. Suitable eyewear, such as glasses having different polarizing or color separations coatings permit the separate images to be seen by one or the other eye. This type of system is expensive and cumbersome because it requires collecting the image from two different views which demands a special camera or two cameras.
U.S. Pat. No. 4,954,890 to Park discloses a representative projector system employing the technique of alternating polarization.
Another technique involves a timed sequence in which images corresponding to right-eye and left-eye perspectives are presented in timed sequence with the use of electronic light valves. U.S. Pat. No. 4,970,486 to Nakagawa, et al., and U.S. Pat. No. 4,877,307 to Kalmanash disclose representative prior art of this type. This time sequence technique also requires the use of eyewear.
There is another example of the timed sequence technique in which the left and right eye views have different polarizations and are viewed not with glasses but with a single polarized screen over both eyes. The screen is formed of a transparent material that has two or more different polarization coatings. U.S. Pat. No. 5,347,644 to Sedlmayr discloses representative prior art of this type.
The timed sequence also requires collecting the image from different views, right eye and left eye.
Alternating polarization and timed sequence stereoscopic techniques both posess the following disadvantages; the image cannot be collected or displayed with convention single view equipment, and eyewear is required for viewing.
It is known that holographic techniques have been used for three dimensional information recording and display. These techniques involve illuminating a three dimensional object with a coherent (laser) beam of light and interfering that light with a reference beam from the same source. The interference pattern is collected on a recording film medium and illumined with the same coherent light from which it was made. The result is a projected image of the object in three dimensions able to be viewed without eyewear. Holographic techniques are not in general use because inherent in them are many limitations: an object has its dimension limited to an extent that it can be illuminated by a laser beam; the object should be stationary; a photograph thereof must be taken in a dark room; and the image cannot be collected and displayed in real time.
Some of the limitations of holography have been addressed by a technique known as composite holography.
Composite holography consists of photographing a three dimensional object in a plurality of different directions under usual illumination such as natural light to prepare a plurality of photographic film sections on which two-dimensional pictorial information is recorded. These two dimensional photographs are information images and are separately illumined with coherent (laser) light and are recorded as holograms. These holograms are then simultaneously illumined with coherent (laser) light producing a projection of the perspective information of the three-dimensional object to be recognized by unaided human eyes at different angles depending upon their position with as much effect as one substantially views the image of the three dimensional object.
Composite holography was limited since the size of the recording medium of the holograms had to be large leading to a large sized overall device making it economically impractical. That limitation was resolved by Takeda et al. as disclosed in U.S. Pat. No. a4,037,919. Also in that disclosure is a detailed description of composite holography.
The disadvantage of composite holography is that it involves photographing the object from many different angles and making a hologram of each of those photographic images. This makes it impossible to collect and display the three dimensional image in real time. A further disadvantage is that it is time consuming, laborious and expensive.
Another example of prior art includes a dual screen system composed of foreground and background screens. The images are collected and projected with incoherent white light. This dual screen system is disclosed in U.S. Pat. No. 3,248,165 to Marks et al.
Referring to FIG. 2 Marks' invention includes two projectors 30 and 31 for projecting two beams of light towards a multiple screen 32. A polarizing filter 33 polarizes the light from projector 30, so that the beam is polarized in the vertical direction as shown by arrow 34. Projector 31 directs its beam of light through a polarizing filter 35 so that the beam which is directed toward the screen arrangement is polarized in a horizontal direction as indicated by arrow 36.
FIGS. 2A, 2B, and 2C illustrate the manner in which the two screens are formed. The foreground screen 37 is formed with a plurality of holes 38 cut in the screen in a symmetrical array.
In the embodiment of FIG. 2D the solid part of the foreground screen is made up of three layers and includes a supporting sheet 39 which is made of some transparent plastic material. On the side facing the projectors, a thin polarizing film 40 is secured for passing rays of light polarized in the direction passed by the polarizing filter having a parallel plane of polarization and for absorbing the rays polarized at right angles thereto. On the back of the sheet 39 a diffuser-reflector film 41 is secured for reflecting the light rays in a diffused manner without changing their plane of polarization. This diffused reflector film is comprised of small aluminum flakes dispersed in a binder. Behind the diffuser-reflector film is a black coating.
The background screen 42 is composed of the same films and layers as the foreground screen 37 except no holes are cut in this screen and the plane of polarization of the polarizing film 40A is at right angles to the polarizing plane of film 40. In the example shown this plane is horizontal.
FIG. 2D illustrates the method in which the two screens cooperate with the two projectors. The two arrows 43 designate rays of two beams of vertically polarized light, one of which strikes a portion of the foreground screen 37 and also rays of two beams 44 polarized in a horizontal direction, one of said rays being directed through a hole 38 in the foreground screen and incident upon the background screen 42. One of the rays 43A from the projector 30 strikes a portion of the foreground screen and penetrates the polarizing film 40, the plastic film 39, and is diffusely reflected by the reflecting sheet 41. The polarizing film 40 is arranged for passing light which is vertically polarized.
A second ray of light 43B from projector 30 passes through one of the holes 38 and is incident upon a polarizing film 40A on the rear screen 42 which is arranged to pass light which is polarized only in the horizontal direction. For this reason light ray 43B is absorbed in film 40A and cannot be seen by the audience. In a like manner, a ray of light 44A, polarized horizontally, strikes polarizing film 40 and is absorbed while another ray 44B from this same projector passes through hole 38, strikes polarizing film 40A, and is transmitted to the diffusing reflecting sheet 41. The reflected light rays 45 are directed toward the audience but only a portion of them pass through holes 38.
It will be obvious from the above description that one portion of the picture will be projected to the background screen 42, where it will be viewed by the audience while another portion of the picture is projected onto the foreground screen 37 where it also will be seen by the audience. In general, the background picture will contain objects that are generally parts of a background such as a distant set of objects or a portion of a room or other enclosure which forms the background of a scene. The foreground screen generally will show the actors or other moving objects which are generally desired to be shown in a position which is closer to the audience. The background screen is on a mechanical motor driven track which enables its distance from the foreground screen to be adjusted.
Marks' dual screen system requires two projectors, one for the foreground image and one for the background image. This is a disadvantage because it is desirable to project the image with conventional single projection equipment so that the extra cost involved in equipping a theatre or home entertainment unit is minimal. It will become obvious that the proposed invention produces a three-dimensional image with a single conventional projection unit.
Marks' system requires two screens to produce apparent depth, a foreground and a background screen. The proposed invention produces apparent depth with a single screen.
Marks' system produces an image with an apparent three dimensional quality of an entire landscape that includes actors and foreground objects on the foreground screen and scenery and background objects on the background screen. The foreground screen is partially transparent because it has holes in it. This partial transparency of the foreground screen gives rise to the apparent depth between the foreground and background. The solid part of the foreground screen and the entire background screen are both opaque to the naked eye. The partial transparency of the foreground screen is, again, due to actual physical holes. If the system were displaying a static scene on the background screen and a moving person or object on the foreground screen and a viewer were looking at the image of person or object on the foreground screen from say, ten feet away, the viewer would see holes in the image of the person or object on the foreground screen and the image would not look real. A disadvantage of this system is that it cannot display a performer on a stage in a small theatre or barroom because the audience is too close and the holes in the screen will be seen. This disadvantage also disqualifies this system to be a small home display where a life size three dimensional display of a person could be used for a video phone display, since the viewer would only be several feet from the screen, and again the holes would be visible.